New Research Challenges Dark Energy: Could Universe Be Slowing?

A groundbreaking study has emerged, suggesting that the universe’s expansion may be slowing rather than accelerating, challenging long-held astronomical assumptions. If validated, this finding could significantly alter our comprehension of dark energy, the mysterious force believed to counteract gravity’s pull in the cosmos.

The idea of an accelerating universe gained traction in 1998 when astronomers studying Type 1a supernovae observed that these distant stars appeared dimmer than expected. They concluded that these supernovae were receding from Earth at an accelerated rate, leading to the Nobel Prize in Physics awarded in 2011. However, the exact nature of dark energy has remained elusive, prompting new investigations into its role in the universe’s expansion.

Recent work by a consortium of researchers utilizing data from the Dark Energy Spectroscopic Instrument (DESI) in Arizona hinted that dark energy might be diminishing over time. This led to the suggestion that the universe’s expansion could eventually decelerate. On November 6, 2023, a new study published in the Monthly Notices of the Royal Astronomical Society supports this notion, offering further evidence that dark energy might not exert the same force as it once did.

Young-Wook Lee, a professor of astrophysics at Yonsei University in South Korea and lead author of the new research, expressed that their results align with the transformative findings from the DESI project, stating, “Our result, in some sense, agrees well with that.” Lee and his team argue that the universe has already started to enter a decelerating phase and that this shift could have profound implications for its ultimate fate.

Lee emphasized, “Dark energy is there, but the present universe has already entered a decelerating phase today. If you can change the fate of the universe, that is really important progress in cosmology.”

To arrive at their conclusions, the researchers examined a sample of 300 galaxies containing Type 1a supernovae. They proposed that the observed dimming of these distant stars results not only from their increasing distance but also from the age of their progenitor stars. Junhyuk Son, a doctoral candidate at Yonsei University and co-author of the study, noted that previous assumptions held that Type 1a supernovae exploded with nearly identical intrinsic brightness. He stated, “However, we found that their luminosity depends on the age of the stars that produce them—younger progenitors yield slightly dimmer supernovae, while older ones are brighter.”

The team claims a high statistical confidence of 99.99 percent regarding the age-brightness relationship, suggesting that Type 1a supernovae can now be used more reliably to evaluate the universe’s expansion. Son remarked, “If confirmed, this would represent the most significant shift in cosmology since the discovery of dark energy in 1998.”

Significantly, if the universe’s expansion continues to decelerate, it could eventually lead to contraction, potentially culminating in what astronomers term the “big crunch.” Lee explained, “That is certainly a possibility. Even two years ago, the Big Crunch was out of the question. But we need more work to see whether it could actually happen.”

Despite the potential implications of this research, skepticism exists within the scientific community. Adam Riess, a professor of physics and astronomy at Johns Hopkins University and a Nobel laureate, criticized the study, stating, “This study rests on a flawed premise.” He contended that current observations indicate supernovae predominantly occur in regions with young star formation, countering the study’s assertions.

Lee countered Riess’s claims, asserting that Type 1a supernovae occur frequently in both old and young galaxies, which he believes undermines the criticisms. He also noted that the age-brightness correlation had been independently validated by two other teams in the United States and China.

Other experts have echoed concerns raised by Riess. Dan Scolnic, an associate professor of physics at Duke University, stated that the study’s leap from host galaxy age to supernova age lacks a solid physical basis. He affirmed, “The universe is still accelerating just fine.” Dillon Brout, an assistant professor at Boston University, acknowledged the importance of questioning existing paradigms but highlighted that the study’s modeling does not align with observational data.

Dragan Huterer, a professor of physics at the University of Michigan, emphasized the need for substantial evidence to support such extraordinary claims, expressing doubt that the current research meets that threshold.

Lee recognizes the controversial nature of their findings and anticipates ongoing debate within the supernova cosmology community. He stated, “We have a long way to go to convince everyone. There are still many people who are strongly against our results.”

Looking ahead, advancements may soon clarify these issues. The Vera C. Rubin Observatory, which commenced operations this year, plans to launch the Legacy Survey of Space and Time in early 2026. This extensive survey will create a detailed time-lapse record of the universe, capturing a wide array of astronomical phenomena every few nights over a decade.

Lee expressed optimism about the Rubin Observatory’s potential, stating it will discover over 20,000 new supernova host galaxies with precise age measurements, allowing for more direct cosmological tests. He concluded, “Dark energy is getting weirder and weirder. I think we are missing something. Maybe, in five years, an even more surprising result can come up.”